C Barca

Anaerobic biofilm reactors for dark fermentative hydrogen production from wastewater: A review

Dark fermentation is a bioprocess driven by anaerobic bacteria that can produce hydrogen (H2) from organic waste and wastewater. This review analyses a relevant number of recent studies that have investigated dark fermentative H2 production from wastewater using two different types of anaerobic biofilm reactors: anaerobic packed bed reactor (APBR) and anaerobic fluidized bed reactor (AFBR). The effect of various parameters, including temperature, pH, carrier material, inoculum pretreatment, hydraulic retention time, substrate type and concentration, on reactor performances was investigated by a critical discussion of the results published in the literature. Also, this review presents an in-depth study on the influence of the main operating parameters on the metabolic pathways. The aim of this review is to provide to researchers and practitioners in the field of H2 production key elements for the best operation of the reactors. Finally, some perspectives and technical challenges to improve H2 production were proposed.

Fermentative hydrogen production in an up-flow anaerobic biofilm reactor inoculated with a co-culture of Clostridium acetobutylicum and Desulfovibrio vulgaris

Dark fermentation systems often show low H2 yields and unstable H2 production, as the result of the variability of microbial dynamics and metabolic pathways. Recent batch investigations have demonstrated that an artificial consortium of two anaerobic bacteria, Clostridium acetobutylicum and Desulfovibrio vulgaris Hildenborough, may redirect metabolic fluxes and improve H2 yields. This study aimed at evaluating the scale-up from batch to continuous H2 production in an up-flow anaerobic packed-bed reactor (APBR) continuously fed with a glucose-medium. The effects of various parameters, including void hydraulic retention time (HRTv), pH, and alkalinity, on H2 production performances and metabolic pathways were investigated. The results demonstrated that a stable H2 production was reached after 3-4days of operation. H2 production rates increased significantly with decreasing HRTv from 4 to 2h. Instead, H2 yields remained almost stable despite the change in HRTv, indicating that the decrease in HRTv did not affect the global metabolism.

Modelling hydrodynamics of horizontal flow steel slag filters designed to upgrade phosphorus removal in small wastewater treatment plants

Steel slag filters, if well designed and operated, may upgrade phosphorus removal in small wastewater treatment plants such as stabilization ponds and constructed wetlands. The main objective of this study was to develop a systemic modelling approach to describe changes in the hydraulic performances and internal hydrodynamics of steel slag filters under real dynamic operating conditions. The experimental retention time distribution curves (RTD curves) determined from tracer experiments performed at different times during the first year of operation of two field-scale steel slag filters were analyzed through a three stage process. First, a statistical analysis of the RTD curves was performed to determine statistical parameters of the retention time distribution. Second, classical tanks in series (TIS) and plug flow with dispersion (PFD) models were used to obtain a first evaluation of the dispersion and mixing regime. Finally, a multi-flow path TIS model, based on the assumption of several flow paths with different hydraulic properties, is proposed to accurately describe the internal hydrodynamics. Overall, the results of this study indicate that higher CaO content, round shape, and larger grain size distribution of steel slag may promote plug-like flow rather than dispersion. The results of the multi-flow path TIS model suggest that the internal hydrodynamics of steel slag filters can be primarily described by two main flow paths: (i) a faster main flow path showing higher plug flow, followed by (ii) a slower secondary flow path showing higher dispersion. The results also showed that internal hydrodynamics may change over time as a consequence of physical-chemical phenomena occurring in the filter, including accumulation of precipitates, slag hydration and carbonation, and particle segregation.